Why do people use 1" pipe on there return pumps?

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salteedogg

Feeder Fish
MFK Member
Feb 13, 2010
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Fort Worth
I have noticed most return pumps are half inch and was wondering why you would need to go bigger then half inch when you plumb it? Wouldn't half inch pipe create more pressure? Reason I ask is because im setting up my sump and I ran half inch tubing off the return pump since the outlet was half inch and after looking online at pictures, I have seen most people use 1 inch instead of half inch. Makes my plumbing look light duty compared to the people who use 1 inch tubing.
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Also wouldn't you lose head flow with bigger pipe due to the weight of water pushing down on the pipe versus half inch pipe with less water? My overflow is a 1 inch diy pvc but return is half inch pvc. I am wondering if this is right since its on a 160 gal
 
You can push more volume thru a larger diameter pipe. That is why the manufactureres suggest to use 1-1/4 diameter to achieve their advertised flowrate. I use 1" spaflex and live with the extra resistance to get cleaner sweeps and less elbows.
 
salteedogg;3902709; said:
I have noticed most return pumps are half inch and was wondering why you would need to go bigger then half inch when you plumb it? Wouldn't half inch pipe create more pressure? Reason I ask is because im setting up my sump and I ran half inch tubing off the return pump since the outlet was half inch and after looking online at pictures, I have seen most people use 1 inch instead of half inch. Makes my plumbing look light duty compared to the people who use 1 inch tubing.
grumble.gif


Also wouldn't you lose head flow with bigger pipe due to the weight of water pushing down on the pipe versus half inch pipe with less water? My overflow is a 1 inch diy pvc but return is half inch pvc. I am wondering if this is right since its on a 160 gal
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Many pumps require a larger size pipe than the outlet size in order to get full flow. I have worked with a lot of irrigation pumps that increase from a 2" outlet to a 6" mainline. The reason to do this is do decrease frictional losses.

When it comes to head pressure the pipe size doesn't matter, the pump will produce the same head height (or p.s.i.) regardless of how big the piping is.

I'm not sure if it would be worthwhile to change out your 1/2" plumbing for 1", the increased flow may or may not be significant. What kind of pump is it and what head height are you pushing against?
 
mag 7 and 5 ft head height...Will it be a problem that I used rubber three quarter inch coming off the mag 7 and then slipped the rubber tubing over my half inch pipe? The rubber tubing fit over my pipe like a glove, but now that I think about it, its like I put a reducer on the line. Hopefully that doesn't mount to anything.
 
Your Mag 7 pump could flow close to 400GPH at 5' head. 400 GPH would give a flow velocity of about 11 feet/second. The calculations for friction loss are complex and the only chart I could find online for flow rate of PVC had a maximum value of about 300 GPH for 1/2".

So, yes, you are constricting the flow by reducing down to 1/2" pipe. You might just use 3/4" flex hose the whole way or use a bushing on your pump to increase the size to 1" right from the pump.
 
There is an excellent pipe size and flow sticky on the DIY forum. Thanks CHOMPERS
 
The calculations for friction loss are complex and the only chart I could find online for flow rate of PVC had a maximum value of about 300 GPH for 1/2".
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This is for a gravity fed flow (i.e. overflow to sump). On the return lines you have a pressurized flow, which can push a much higher flow rate through the pipe. The same volume flowing through a smaller pipe will have a greater flow velocity than in a larger pipe.

Check out this chart for more info on pressurized flow rates.
 
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